Olefin resins such as polyolefins and polyolefin elastomers are used in various fields including the manufacture of shaped articles because of their excellent properties, for example mechanical properties. In recent years, the requirements for the properties of these olefin resins have been diversified. Such diverse requirements have resulted in the need of olefin resins having various properties, for example olefin resins having excellent rigidity as well as high impact strength, weathering resistance, heat resistance, cold resistance, crosslinking efficiency, oil resistance, adhesion, dyeability, wettability and compatibility with other polar-group containing resins.
To achieve these properties, it is necessary that functional groups having excellent crosslinking efficiency and modification efficiency as well as cyclic structures be introduced into the polymer chains. An economically advantageous process for producing such polymers is, for example, to copolymerize olefins with diene monomers or to copolymerize α-olefins such as ethylene with cyclic olefins.
Processes for introducing functional groups that have excellent crosslinking efficiency and modification efficiency into polymer chains are disclosed in, for example, European Patent Application No. 0275676 (EP0275676) (1988) (Patent Literature 1), Makromol. Chem. 1991, (192), 2591 (Non-Patent Literature 1), U.S. Pat. No. 6,310,164 (U.S. Pat. No. 6,310,164) (2001) (Patent Literature 2) and JP-A-H11-080269 (Patent Literature 3).
However, these processes disclosed in the art have drawbacks. For example, a sufficient amount of vinyl groups cannot be introduced in the copolymer, or unsaturated bonds in the main chain lower properties such as weathering resistance, heat resistance and ozone resistance. Further, a sufficient molecular weight cannot be obtained, resulting in poor mechanical properties.
Macromolecules 2003 (36), 9067 (Non-Patent Literature 2) discloses a method for synthesizing an ethylene/butadiene copolymer that contains a vinyl group and is free of 1,4-addition units in the main chain. However, the main chain contains unsaturated bonds derived from 1,3-addition units, which may cause adverse effects on properties. Further, the method of Non-Patent Literature 2 produces vinyl groups only when the ethylene/butadiene feed ratio is very low, namely, when butadiene is fed in a large amount. However, such conditions extremely decrease the polymerization activity, resulting in economical disadvantages in commercial production. Furthermore, Non-Patent Literature 2 does not describe any data of molecular weight measurement.
Meanwhile, polyolefin elastomers that have unsaturated bonds inside chains and no unsaturated bonds in the main chain are known in the art, with examples including ethylene/propylene/diene monomer copolymers (EPT, EPDM) in which the diene monomer is, for example, ethylidene norbornene, vinyl norbornene or dicyclopentadiene. When these polyolefin elastomers are used as rubber shaped articles, they are subjected to peroxide crosslinking or radical modification. In a usual crosslinking method, a rubber extrudate containing a vulcanizing agent is crosslinked batchwise under a pressurized steam atmosphere or is crosslinked continuously under hot air.
However, because the unsaturated bonds in EPT and EPDM copolymers are less reactive than the vinyl group, the peroxide crosslinking reaction involves a large amount of peroxides. When a rubber extrudate is crosslinked under pressurized steam or hot air (hereinafter, such crosslinking will be referred to as hot air crosslinking) in the presence of an organic peroxide, the contact of air (oxygen) with the surface of the rubber extrudate induces a decomposition reaction of the resin main chain. Consequently, the crosslinking does not proceed sufficiently and at the same time the rubber undergoes softening degradation, resulting in a crosslinked product having a sticky surface. Further, the properties of the crosslinked copolymers are often unsatisfactory for the reasons such as residual peroxides in excessively large amounts. Thus, there has been a need for new polyolefin elastomers that can be crosslinked by hot air crosslinking with organic peroxides.
Since ethylidene norbornene, vinyl norbornene and the like have a high boiling point, removing the unreacted diene monomers after the copolymerization consumes large amounts of energy, causing economic disadvantages.
Thus, there has been a need for polyolefin elastomers which use inexpensive and low-boiling general diene monomers such as 1,3-butadiene and which have double bonds in side chains and are free of unsaturated bonds in the main chain. An economically advantageous process for producing such polyolefin elastomers is also desired.
However, a limited number of references have disclosed copolymers which have double bonds and are free of unsaturated bonds in the main chain, and production processes for such copolymers. In detail, only JP-A-2005-200503 (Patent Literature 4) and J. Am. Chem. Soc. 2005 (127), 5774 (Non-Patent Literature 3) disclose propylene/butadiene copolymers. Further, copolymers produced by the processes disclosed in Patent Literature 4 and Non-Patent Literature 3 have a low molecular weight and consequent insufficient mechanical properties.
Acyclic structure may be introduced into a polymer chain by polymerizing a cyclic olefin such as norbornene in the presence of a vanadium-containing catalyst formed of a soluble vanadium compound and an organoaluminum compound. However, this catalyst system can catalyze copolymerization of a limited variety of cyclic olefins, has low polymerization activity and cannot afford copolymers having a sufficient molecular weight and a sufficient cyclic olefin content. Further, large amounts of energy are required to remove unreacted cyclic olefins after the reaction, thereby resulting in economic disadvantages.
J. Am. Chem. Soc., 2005 (127), 4582 (Non-Patent Literature 4) and Tetrahedron, 2004 (60), 7147 (Non-Patent Literature 5) disclose ethylene/cyclic olefin (cyclopentene, cyclohexene, cycloheptene, cyclooctene) copolymerization by a half metallocene/aluminoxane catalyst. Further, Macromolecules, 2002 (35), 9640 (Non-Patent Literature 6) discloses ethylene/cyclopentene copolymerization by a bisphenoxyimine complex/aluminoxane catalyst. However, these catalyst systems have a low incorporation efficiency for cyclic olefins. To obtain a polymer having a high cyclic olefin content, the cyclic olefin has to be fed in a large amount. Thus, the polymerization activity is insufficient.
Alternatively, acyclic structure may be introduced into a main chain by copolymerizing an olefin with a diene monomer.
Such methods are disclosed in JP-A-H11-080269 (Patent Literature 5) and JP-A-2004-018697 (Patent Literature 6). However, the copolymers obtained by these methods contain unsaturated bonds in the main chain which lower properties such as weathering resistance, heat resistance and ozone resistance.
Further, the synthesis of ethylene/butadiene copolymers having a cyclic structure in the main chain is disclosed in Macromolecular Symposia, 2006, (234), 1288 (Non-Patent Literature 7), Macromolecular Chemistry and Physics, 2006, (207), 304 (Non-Patent Literature 8), Macromolecules, 2005, 38, 5493 (Non-Patent Literature 9), Macromolecules, 2004 (37), 238 (Non-Patent Literature 10), Macromolecules, 2003 (36), 9067 (Non-Patent Literature 11) and Journal of the American Chemical Society, 2002, (124), 3502 (Non-Patent Literature 12). However, the copolymers obtained by the disclosed methods contain unsaturated bonds in the main chain that are derived from 1,4-addition units and 1,3-addition units, possibly leading to adverse effects on properties. Further, the above references do not describe any data of molecular weight measurement.
Journal of the American Chemical Society, 2003, (125), 8970 (Non-Patent Literature 13) discloses a process for synthesizing an ethylene/butadiene copolymer which has a cyclic structure in the main chain and is free of unsaturated bonds derived from 1,4-addition units and 1,3-addition units. According to the process, however, the polymerization activity is insufficient and the obtainable molecular weight is low. Thus, the process is not suited for commercial production.